Control Box Diagnostics & Keypad Replacement (UNDERHOOD DTM)

Technical Support Subject Control Box Diagnostics & Keypad Replacement (UNDERHOODTM & DTM) Document Version Department Revision Details Revised by Tech Engineering Implemented EXT-ALL-026 A Tech Document Release BDJ 17 Aug 2021 RB N/A 17 Aug 2021 Knowledge Base: kb.vmacair.com Page 1 of 4 Email: tech@vmacair.com Web: www.vmacair.com Technical Support: 1(888)241-2289 Toll Free:1(800)738-8622 Fax: 1(877)740-3201 System or Parts affected UNDERHOODTM 70/150 Direct Transmission Mount: DTM & DTM-H • P/N# 3550723 VR Control Box • P/N# 3550727 VR Control Box • P/N# 3550848 Control Box, DTM • P/N# 3550779 Replacement Keypad OVERVIEW The control box serves as the operator’s control panel and contains the “ON/OFF” button, “READY” and “WARNING” lights, and the Liquid Crystal Display (LCD) which includes information such as compressor hours, service reminders, warning messages, error codes, and diagnostic information. If the control box does not function as per design, the following steps should be taken. The VMAC digital control box “Remote Start/Stop wires” can be used to diagnose if the entire control box is faulty or the keypad is the problem. Inspect the control box Inspect the control box for physical damage. The ON and OFF buttons are microswitches beneath a flexible membrane. If the membrane is damaged the switch(es) could be contaminated and may not work properly. Contamination can result in switch that can be stuck in a state where it is always making contact or won’t make contact at all. Confirm power and ground to the control box With key switched power and a ground supplied to the control box, the LCD should be back-lit and it should display characters.  A minimum of 12 volts is required for the LCD to function. Confirm that there is sufficient voltage and a good ground to the display box. Locate the flat white 4 pin interface connector in the harness from the control box.  With vehicle’s key switch off, using a multimeter check for good continuity (